Species Spotlight: Horseshoe Crabs

Learn more about this resident of our Living Seashore exhibit!

Published June 29, 2018

Horseshoe crabs are native to the coast of the Atlantic Ocean throughout North America. Females often grow to be larger than males, typically averaging about 18 to 19 inches from head to tail, compared to 14 to 15 inches for males.

The distinct appearance of the horseshoe crab comes from its dark brown shell and its long tail, which is called a telson. The telson may look menacing, but it is actually harmless; the horseshoe crab uses it to flip itself over when on its back. If you come across an upside-down horseshoe crab on the beach, never grab its telson—you could harm the animal. Instead, gently grab either side of its shell and flip it over.

Often referred to as “living fossils," the ancestors of horseshoe crabs can be traced back to about 445 million years ago! Throughout all this time, not much about the horseshoe crab’s anatomy has changed. The horseshoe crab has not one, not two, but 10 eyes—and each of them are scattered throughout its body! Its brain can be found in a thin circle around its mouth, which is located on the horseshoe crab’s underside and is surrounded by bristles that are used to chew food.

Despite the “crab” part of the horseshoe crab’s name, this species is closer related to spiders and scorpions rather than crustaceans.